Negative electrode active material and preparation method thereof, secondary battery and electric device

Abstract

The invention provides a negative electrode active material and a preparation method thereof, a secondary battery and an electric device, and relates to the field of lithium batteries. The secondary battery comprises a negative electrode plate, the negative electrode plate comprises a negative electrode film layer, the negative electrode film layer comprises a negative electrode active material, the negative electrode active material comprises a carbon core and a nitrogen-doped porous carbon layer coating the surface of the carbon core, and the nitrogen-doped porous carbon layer comprises pyrrole nitrogen, pyridine nitrogen and mesopores; wherein the volume of the mesopores accounts for 40-90% of the total pore volume of the negative electrode active material; the mass ratio of the total nitrogen content in the negative electrode active material is 0.4%-3%, and the mass ratio of the pyrrole nitrogen and the pyridine nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%. The secondary battery has good fast charging performance.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a negative electrode active material and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As the application range of batteries becomes wider and wider, the requirements for the performance of secondary batteries are becoming increasingly stringent.

[0003] At present, the fast charging performance of secondary batteries still needs to be further improved. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode active material and a preparation method thereof, a secondary battery and an electrical device, so as to effectively improve the fast charging performance of the secondary battery.

[0005] A first aspect of the present application provides a secondary battery, which includes a negative electrode plate, wherein the negative electrode plate includes a negative electrode film layer;

[0006] The negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a carbon core and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, the nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridinic nitrogen and mesopores;

[0007] Among them, the volume proportion of mesopores in the total pore volume of the negative electrode active material is 40%-90%;

[0008] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by weight, and the pyrrolic nitrogen and pyridinic nitrogen together account for 30%-80% by weight of the total nitrogen content in the negative electrode active material.

[0009] In the secondary battery provided in the present application, the introduced negative electrode active material has high nitrogen doping while taking into account high mesoporous content, and the high nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyridinic nitrogen. Therefore, the high mesoporous content is utilized to effectively improve the wettability of the negative electrode active material, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, and the high nitrogen doping is utilized to improve the adsorption capacity of the negative electrode active material for lithium ions. In addition, the desolvation rate of the solvated lithium ions and the lithium ion diffusion rate are improved by utilizing the rich pyrrolic nitrogen and pyridinic nitrogen. The combined effect of the three accelerates the kinetic process during the charging process of the secondary battery, and effectively improves the fast charging performance of the secondary battery.

[0010] In any embodiment, the contact angle of the negative electrode active material is 10° to 38.5°.

[0011] The above-mentioned negative electrode active material has a small contact angle with the electrolyte and good wettability, which is beneficial to improving the fast charging capability and cycle performance of the secondary battery.

[0012] In any embodiment, the nitrogen-doped porous carbon layer contains micropores and macropores, the micropores, macropores and mesopores are at least partially interconnected, and the total volume of the micropores and macropores accounts for 10%-60% of the total pore volume of the negative electrode active material. By at least partially interconnecting the micropores, macropores and mesopores, and controlling the total volume of the micropores and macropores to account for 10%-60% of the total pore volume of the negative electrode active material, the pore structure of the material can be effectively improved by working together with the mesopores, which is beneficial to improving the contact angle of the negative electrode active material, improving the wettability, and improving the fast charging performance of the battery.

[0013] In any embodiment, the mass proportion of pyrrolic nitrogen in the total nitrogen content of the negative electrode active material is 12%-40%; and / or the mass proportion of pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 15%-45%.

[0014] By controlling the pyrrolic nitrogen and pyridinic nitrogen content within the above-mentioned relatively high content range, it is beneficial to improve the desolvation rate of the solvated lithium ions and the diffusion rate of the lithium ions, thereby improving the fast charging performance of the secondary battery.

[0015] In any embodiment, the mass percentage of pyrrolic nitrogen and pyridinic nitrogen in the negative electrode active material is 0.3%-0.9%; and / or,

[0016] The mass percentage of pyrrolic nitrogen in the negative electrode active material is 0.1%-0.4%; and / or,

[0017] The mass proportion of pyridinic nitrogen in the negative electrode active material is 0.2%-0.5%.

[0018] By controlling the pyrrolic nitrogen and pyridinic nitrogen within the above-mentioned relatively high content range, it is beneficial to improve the desolvation rate of the solvated lithium ions and the diffusion rate of the lithium ions, thereby enhancing the fast charging performance of the secondary battery.

[0019] In any embodiment, the nitrogen-doped porous carbon layer comprises graphitic nitrogen and nitrogen oxides; wherein the mass proportion of graphitic nitrogen in the total nitrogen content of the negative electrode active material is 10%-30%.

[0020] Controlling the mass proportion of graphite nitrogen in the total nitrogen content of the negative electrode active material within the above range is beneficial to making the mass proportion of the total content of pyridinic nitrogen and pyrrolic nitrogen in the total nitrogen content 30%-70%, thereby improving the fast charging performance of the secondary battery.

[0021] In any embodiment, the negative electrode active material satisfies at least one of (a1) to (a6):

[0022] (a1) The volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm;

[0023] (a2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g;

[0024] (a3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0025] (a4) the carbon core comprises at least one of artificial graphite and natural graphite;

[0026] (a5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

[0027] Controlling the negative electrode active material to satisfy at least one of (a1)-(a5) is beneficial to improving the fast charging performance of the secondary battery.

[0028] In any embodiment, the carbon core comprises secondary graphite particles, and the volume particle size distribution Dv50 of the secondary graphite particles is 9 μm-22 μm; or,

[0029] The carbon core includes graphite single particles, and the volume particle size distribution Dv50 of the graphite single particles is 5μm-10μm.

[0030] Secondary graphite particles have rich orientations but poor structural stability. Therefore, using secondary graphite particles within the above-mentioned particle size range as the carbon core is beneficial to improving the compaction density of the negative electrode plate and facilitating the infiltration of the core with the electrolyte, so that the secondary battery has both better energy density and fast charging performance.

[0031] Graphite single particles have a stable structure but poor wettability, so selecting a particle size within the aforementioned smaller range is beneficial for improving the fast charging performance of secondary batteries while improving the cycle performance.

[0032] In any embodiment, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2):

[0033] (b1) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-9.0m 2 / g;

[0034] (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, the micropores and the mesopores are at least partially interconnected, the volume of the micropores accounts for 0-25% of the total pore volume, and / or the volume of the mesopores accounts for 63%-90% of the total pore volume.

[0035] Controlling the negative electrode active material composed of a nitrogen-doped porous soft carbon layer covering a carbon core to satisfy at least one of (b1)-(b2) is beneficial to improving the wettability of the negative electrode active material and improving the battery fast charging performance and cycle performance.

[0036] In any embodiment, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1)-(c2):

[0037] (c1) The specific surface area of ​​the negative electrode active material is 4.0 m 2 / g-10.5m 2 / g;

[0038] (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, the micropores and the mesopores are at least partially interconnected, the volume of the micropores accounts for 25%-50% of the total pore volume, and / or the volume of the mesopores accounts for 40%-85% of the total pore volume. Controlling the negative electrode active material composed of a nitrogen-doped porous hard carbon layer coated with a carbon core to meet at least one of (c1)-(c2) is beneficial to improving the wettability of the negative electrode active material, improving the fast charging performance and cycle performance of the battery.

[0039] In any embodiment, the single surface density of the negative electrode film layer is 100 mg / cm 2 -200mg / cm 2 and / or,

[0040] The compaction density of the negative electrode film is 1.3g / cm 3 -1.8g / cm 3 and / or,

[0041] The porosity of the negative electrode film layer is 20%-35%.

[0042] Controlling the single-surface surface density of the negative electrode film layer within the above range is beneficial to the diffusion of lithium ions in the negative electrode film layer and can effectively inhibit lithium precipitation, which can more effectively improve the fast charging performance and cycle performance of the secondary battery. Controlling the negative electrode film layer to be within the above-mentioned higher compaction density range can effectively improve the energy density of the secondary battery on the basis of fast charging performance, which is beneficial to high-rate charging. Controlling the porosity of the negative electrode film layer within the above range is beneficial to making the negative electrode film layer more fully infiltrated by the electrolyte during the cycle, which is beneficial to improving fast charging and cycle performance, and is beneficial to achieving charging and discharging at a large rate.

[0043] In any embodiment, the absorption rate of the negative electrode plate for the E324 electrolyte is 0.5 mg / s 1 / 2 ~4 mg / s 1 / 2 .

[0044] The above-mentioned negative electrode plate has a high liquid absorption rate, which can improve the wetting efficiency of the electrolyte on the negative electrode plate, improve the ion transmission path, reduce the interface resistance, and improve the fast charging performance of the secondary battery.

[0045] The second aspect of the present application further provides an electrical device, which includes the secondary battery provided by the first aspect of the present application.

[0046] The third aspect of the present application also provides a negative electrode active material, the negative electrode active material includes a carbon core and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, the nitrogen-doped porous carbon layer includes pyrrolic nitrogen, pyridinic nitrogen and mesopores;

[0047] Among them, the volume proportion of mesopores in the total pore volume of the negative electrode active material is 40%-90%;

[0048] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by weight, and the pyrrolic nitrogen and pyridinic nitrogen together account for 30%-80% by weight of the total nitrogen content in the negative electrode active material.

[0049] Therefore, the negative electrode active material provided by the present application achieves high nitrogen doping while taking into account high mesoporous content, and the nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyridinic nitrogen. Therefore, the high mesoporous content is utilized to effectively improve the wettability of the negative electrode active material, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, and the high nitrogen doping is utilized to improve the adsorption capacity of the negative electrode active material for lithium ions. In addition, the desolvation rate of the solvated lithium ions and the lithium ion diffusion rate are improved by utilizing the rich pyrrolic nitrogen and pyridinic nitrogen. The combined effect of the three accelerates the kinetic process during the charging process of the secondary battery and effectively improves the fast charging performance of the secondary battery.

[0050] In any embodiment, the negative electrode active material satisfies at least one of (d1) to (d5):

[0051] (d1) The volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm;

[0052] (d2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g;

[0053] (d3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0054] (d4) the carbon core comprises at least one of artificial graphite and natural graphite;

[0055] (d5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

[0056] Controlling the negative electrode active material to satisfy at least one of (d1)-(d5) is beneficial to improving the fast charging performance of the secondary battery.

[0057] A fourth aspect of the present application provides a method for preparing a negative electrode active material, comprising:

[0058] After mixing the high nitrogen polymer and the carbon core, carbonization is carried out in an inert atmosphere;

[0059] Among them, the total nitrogen mass content in the high nitrogen polymer is ≥0.8%, and the high nitrogen polymer includes pyrrolic nitrogen and pyridinic nitrogen. The mass content of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 40%-90%.

[0060] The preparation method provided in the present application selects a high-nitrogen polymer rich in pyridinic nitrogen and pyrrolic nitrogen as a carbon source and a nitrogen source, directly mixes it with a carbon core and then carbonizes it, which is beneficial in the preparation process, so that part of the nitrogen in the high-nitrogen polymer overflows to increase the mesopores of the negative electrode active material, and the remaining nitrogen is doped in the formed carbon layer and tends to form pyridinic nitrogen and pyrrolic nitrogen. Not only is the nitrogen doping and mesopore distribution in the prepared negative electrode active material more uniform, but the mesopore content and nitrogen doping amount in the negative electrode active material are also simultaneously improved, and the nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyrrolic nitrogen. The high mesopore content is used to effectively improve the wettability of the negative electrode active material, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, the high nitrogen doping is used to improve the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrolic nitrogen and pyridinic nitrogen are used to improve the desolvation rate of the solvated lithium ions and the lithium ion diffusion rate. The combined effect of the three accelerates the kinetic process during the charging process of the secondary battery, and effectively improves the fast charging performance of the secondary battery.

[0061] In any embodiment, the preparation method satisfies at least one of (e1) to (e3):

[0062] (e1) the high nitrogen polymer includes at least one of a high nitrogen asphalt and a high nitrogen copolymer;

[0063] (e2) The carbonization temperature is 700°C-1300°C, and the carbonization time is 6h-15h;

[0064] (e3) The mass ratio of the high nitrogen polymer to the carbon core is 100:2-20.

[0065] By controlling the preparation method to satisfy at least one of (e1)-(e3), it is advantageous to prepare negative electrode active materials that have both high mesoporous content and high nitrogen doping, thereby improving the fast charging of secondary batteries.

[0066] In any embodiment, the high nitrogen polymer is a high nitrogen copolymer;

[0067] Wherein, the nitrogen mass content in the high nitrogen copolymer is 1%-5%; and / or,

[0068] The carbonization temperature is 1000°C-1100°C; and / or,

[0069] High nitrogen copolymers include acrylic acid-acrylonitrile copolymers.

[0070] Under the condition of selecting the high nitrogen polymer as the high nitrogen copolymer, by controlling the nitrogen mass content and / or the insulation temperature within the above range, it is beneficial to carbonize the high nitrogen copolymer to form a nitrogen-doped porous hard carbon coating layer coated on the surface of the carbon core. Combined with the insulation time, the carbonization depth is within a suitable range, so as to obtain a negative electrode active material that has both high mesoporous content and high nitrogen doping, which is beneficial to improving the fast charging performance of the battery.

[0071] In any embodiment, the high nitrogen polymer is high nitrogen asphalt;

[0072] Wherein, the nitrogen content of high nitrogen asphalt is 0.8%-4% by mass; and / or,

[0073] The insulation temperature is 900℃-1300℃.

[0074] When the high-nitrogen polymer is selected as high-nitrogen asphalt, by controlling the nitrogen mass content and / or the insulation temperature within the above range, it is beneficial to carbonize the high-nitrogen asphalt to form a nitrogen-doped porous soft carbon coating layer coated on the surface of the carbon core. Combined with the insulation time, the carbonization depth is within an appropriate range, and a negative electrode active material that has both high mesoporous content and high nitrogen doping is obtained, which is beneficial to improving the fast charging performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0076] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0077] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0078] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0079] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0080] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0081] Description of reference numerals:

[0082] 1-battery pack; 2-upper box; 3-lower box; 4-battery module; 5-battery cell; 51-housing; 52-electrode assembly; 53-top cover assembly. DETAILED DESCRIPTION

[0083] Hereinafter, the negative electrode active material and its preparation method, secondary battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0084] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0085] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0086] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0087] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0088] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, "include" and "comprising" may represent that other components not listed may also be included or only listed components may be included or only listed components may be included.

[0089] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0090] As the application scope of secondary batteries becomes wider and wider, people have put forward severe challenges to the performance of secondary batteries. At present, the fast charging performance of secondary batteries still needs to be further improved.

[0091] Since the key to improving the fast charging capability of secondary batteries lies in improving the performance of negative electrode active materials and negative electrode sheets. During the charging process of secondary batteries, taking carbon-coated graphite as an example, the electrode kinetics process usually includes the following steps: (1) Diffusion of solvated lithium ions in the electrolyte; (2) The solvated lithium ions that reach the surface of the graphite negative electrode begin to desolvate; (3) The desolvated lithium ions pass through the solid electrolyte (SEI) membrane, the carbon coating layer, and are embedded in the graphite interlayer with charge transfer; (4) The lithium ions diffuse inside the graphite particles.

[0092] Based on this, a first aspect of the embodiment of the present application provides a secondary battery, which includes a negative electrode plate, and the negative electrode plate includes a negative electrode film layer;

[0093] The negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a carbon core and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, the nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridinic nitrogen and mesopores;

[0094] Among them, the volume proportion of mesopores in the total pore volume of the negative electrode active material is 40%-90%;

[0095] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by weight, and the pyrrolic nitrogen and pyridinic nitrogen together account for 30%-80% by weight of the total nitrogen content in the negative electrode active material.

[0096] Pyridinic nitrogen and pyrrolic nitrogen refer to the bonding mode of nitrogen atoms to the graphite lattice. Pyridinic nitrogen refers to the nitrogen atom connected to two carbon atoms at the edge of the graphite surface, which provides a p electron to the conjugated π system to cause p-doping; pyrrolic nitrogen refers to the nitrogen atom connected to two carbon atoms on the graphite surface to form a five-membered ring, which provides 2 p electrons to the conjugated π system to cause p-doping.

[0097] In this application, the composition of pyrrole nitrogen and pyridinic nitrogen and the mass proportion of the total nitrogen content can be characterized and confirmed by an X-ray photoelectron spectroscopy (XPS) instrument. Specifically, the powder scraped off the surface of the negative electrode plate is roasted to remove the binder, conductive agent, etc., to obtain the negative electrode active material, and the test is carried out by using an X-ray photoelectron spectroscopy (XPS) instrument with an X-ray source of Al target Kα radiation with hν of 1486.6eV. N1s is peaked at 399.5eV and 398.5eV, and the pyrrole nitrogen area proportion and pyridinic nitrogen area proportion are calculated respectively. The pyrrole nitrogen area proportion is the mass proportion of pyrrole nitrogen in the total nitrogen content of the negative electrode material, and the pyridinic nitrogen area proportion is the mass proportion of the pyridinic nitrogen group in the total nitrogen content of the negative electrode material.

[0098] In the present application, the test method for the volume ratio of mesopores in the total pore volume of the negative electrode active material includes: calcining the powder scraped from the surface of the negative electrode plate to remove the binder, conductive agent, etc., to obtain a negative electrode active material sample, placing the negative electrode active material sample in a gas adsorption analyzer at -196°C for testing, and obtaining an isothermal adsorption-desorption curve. N adsorption at relative pressure 0.99 2 The gas volume is equivalent to the total pore volume. Then, according to the volume distribution corresponding to different pore sizes in the micropore and mesopore range, the isothermal adsorption curve is analyzed by the Horvath-Kawazoe (HK) method to obtain the proportion of the volume of mesopores to the total pore volume.

[0099] For negative electrode active materials, according to the pore size, the pore size of mesopores is 2nm≤≤50nm, which is more conducive to the transmission of solvated lithium ions than micropores, and the mesopore content is positively correlated with the wettability. However, if the content is too large, the mechanical properties are poor, and the kinetic properties and cycle performance are easily deteriorated due to breakage. Therefore, the content of mesopores is controlled within the above range. On the basis of the nitrogen-doped carbon coating having better mechanical properties, it not only provides more lithium ion embedding channels and shortens the lithium ion transmission distance, but also provides multi-dimensional open permeation channels, enhances the wettability of the electrolyte, and makes it easier for the solvated lithium ions in the electrolyte to diffuse to the surface of the graphite particles, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, and accelerate the liquid phase mass transfer step in the electrolyte phase.

[0100] The total nitrogen content in the negative electrode active material is controlled to account for 0.4%-3% by weight, and the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%. High nitrogen doping is used to improve the adsorption capacity of the negative electrode active material for lithium ions, and nitrogen doping is used to enrich pyrrolic nitrogen and pyridinic nitrogen. On the one hand, pyrrolic nitrogen and pyridinic nitrogen are used to induce the formation of SEI during the chemical film formation process, forming a SEI with more inorganic components-lithium nitride (LiN). 3 N), this inorganic component SEI is compared with Li 2 CO 3 The higher adsorption energy makes it easier for lithium ions to diffuse to the surface. At the same time, this type of inorganic component SEI has a lower desolvation energy barrier, which accelerates the reduction of the transfer impedance of lithium ions in the coating layer and accelerates the desolvation step of the solvated lithium ions. On the other hand, pyridinic nitrogen and pyrrolic nitrogen have lone pairs of electrons in their heterocyclic structures, which makes them show higher reactivity in electrochemical and catalytic applications. They can more efficiently adsorb lithium ions during charging and discharging, reduce the desolvation energy barrier, and reduce Li + The mass transfer resistance is reduced and the lithium ion diffusion capacity of the coating layer is improved, thereby accelerating the diffusion of desolvated lithium ions in the graphite coating layer.

[0101] It is understandable that, based on the above reasons, if the total content of pyrrole nitrogen and pyridinic nitrogen, or the total nitrogen content is too low, the effect of improving the desolvation rate of solvated lithium ions and the lithium ion diffusion rate will be limited. If it is too large, it will lead to SEI thickening, affecting the initial effect of the secondary battery and the long-term performance of the secondary battery. Therefore, in this application, the total nitrogen content in the negative electrode active material is controlled to account for 0.4%-3% by mass, and the mass proportion of pyrrole nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%.

[0102] In summary, the secondary battery provided by the present application introduces a negative electrode active material that has a high mesoporous content while achieving high nitrogen doping, and the high nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyridinic nitrogen. Therefore, the high mesoporous content is utilized to effectively improve the wettability of the negative electrode active material and shorten the lithium ion transmission distance, and the high nitrogen doping is utilized to improve the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrolic nitrogen and pyridinic nitrogen are utilized to improve the lithium ion diffusion rate, and the introduction of defect sites to improve the wettability of the negative electrode active material. The combined effect of the three improves the wettability of the negative electrode active material and constructs a migration path for rapid lithium ion transmission, thereby effectively improving the fast charging performance of the secondary battery.

[0103] Exemplarily, the volume fraction of mesopores in the total pore volume of the negative electrode active material is any one of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90%, or between any two values.

[0104] Illustratively, the mass percentage of the total nitrogen content in the negative electrode active material is any value among 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0% or between any two values.

[0105] Exemplarily, the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or between any two values.

[0106] In some embodiments, the contact angle of the negative electrode active material is 10°-38.5°.

[0107] Among them, in this application, the contact angle test method includes: placing the powder to be tested in a blast oven at 65°C for 2 hours, and then fixing it on the SDC-200 contact angle tester; dripping 11μL of test electrolyte contact angle on the surface to ensure that the droplet shape is stable, the system records 100 photos and then selects the 80th photo, and uses the tester supporting software SDC-200 to fit the contact angle as a measurement value; in this application, the same sample is tested continuously for 6 times at different points, and 4 similar numerical values ​​are selected for output to ensure the reliability of the test results.

[0108] The above-mentioned negative electrode active material has a small contact angle with the electrolyte and good wettability, which is beneficial to improving the fast charging capacity and cycle performance of the secondary battery.

[0109] Illustratively, the contact angle of the negative electrode active material is any one of 10°, 12°, 15°, 17°, 20°, 23°, 25°, 28°, 30°, 32°, 35°, 38°, 38.5°, or between any two values.

[0110] In some embodiments, the nitrogen-doped porous carbon layer contains micropores and macropores, the micropores, macropores and mesopores are at least partially interconnected, and the total volume of the micropores and macropores accounts for 10%-60% of the total pore volume of the negative electrode active material.

[0111] The test method for the proportion of the volume of micropores and macropores to the total pore volume includes: placing the negative electrode active material sample in a gas adsorption analyzer at -196°C for testing, and obtaining an isothermal adsorption-desorption curve. 2 The gas volume is equivalent to the total pore volume. Then, according to the volume distribution corresponding to the pore size within the micropore range, the isothermal adsorption curve is analyzed by the Horvath-Kawazoe (HK) method to obtain the proportion of the volume of micropores to the total pore volume.

[0112] According to the pore size, the pore size of micropores is less than 2nm, and the pore size of macropores is greater than 50nm.

[0113] By at least partially interconnecting the micropores, macropores and mesopores, and controlling the total volume of the micropores and macropores to account for 10%-60% of the total pore volume of the negative electrode active material, the pore structure of the material can be effectively improved together with the mesopores, which is beneficial to improving the contact angle of the negative electrode active material, improving the wettability, and improving the fast charging performance and cycle performance of the battery.

[0114] Exemplarily, the total volume of micropores and macropores accounts for any value of 10%, 15%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% of the total pore volume of the negative electrode active material, or between any two values.

[0115] In some embodiments, the mass proportion of pyrrolic nitrogen in the total nitrogen content of the negative electrode active material is 12%-40%; and / or the mass proportion of pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 15%-45%.

[0116] Controlling the mass proportion of pyrrolic nitrogen and / or pyridinic nitrogen in the total nitrogen content of the negative electrode active material to be within the above-mentioned relatively high range is beneficial to improving the desolvation rate of solvated lithium ions and the diffusion rate of lithium ions, thereby enhancing the fast charging performance of the secondary battery.

[0117] Exemplarily, the mass proportion of pyrrolic nitrogen in the total nitrogen content of the negative electrode active material is any one of 12%, 15%, 20%, 25%, 30%, 35%, 40%, or between any two values.

[0118] Exemplarily, the mass proportion of pyridinic nitrogen in the total nitrogen content of the negative electrode active material is any one of 15%, 20%, 25%, 30%, 35%, 40%, 45%, or between any two values.

[0119] In some embodiments, the mass percentage of pyrrolic nitrogen and pyridinic nitrogen in the negative electrode active material is 0.3%-0.9%; and / or,

[0120] The mass percentage of pyrrolic nitrogen in the negative electrode active material is 0.1%-0.4%; and / or,

[0121] The mass proportion of pyridinic nitrogen in the negative electrode active material is 0.2%-0.5%.

[0122] By controlling the pyrrolic nitrogen and pyridinic nitrogen within the above-mentioned relatively high content range, it is beneficial to improve the desolvation rate of the solvated lithium ions and the diffusion rate of the lithium ions, thereby enhancing the fast charging performance of the secondary battery.

[0123] Exemplarily, the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the negative electrode active material is any one of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or between any two values.

[0124] Exemplarily, the mass proportion of pyrrolic nitrogen in the negative electrode active material is any one of 0.1%, 0.2%, 0.3%, 0.4%, or between any two values.

[0125] Exemplarily, the mass proportion of pyridinic nitrogen in the negative electrode active material is any one of 0.2%, 0.3%, 0.4%, 0.5%, or between any two values.

[0126] In some embodiments, the nitrogen-doped porous carbon layer includes graphitic nitrogen and oxynitride; wherein the mass proportion of graphitic nitrogen in the total nitrogen content of the negative electrode active material is 10%-30%.

[0127] Graphitic nitrogen refers to the bonding mode of nitrogen atoms to the graphite lattice. Graphitic nitrogen refers to the situation where nitrogen atoms are connected to three carbon atoms, which will provide an n electron to the conjugated π system and thus cause n-doping of graphite.

[0128] In this application, the composition of graphite nitrogen and the mass proportion of the total nitrogen content can be characterized and confirmed by an X-ray photoelectron spectroscopy (XPS) instrument. Specifically, the powder scraped from the surface of the negative electrode plate is roasted to remove the binder, conductive agent, etc., to obtain the negative electrode active material, and the test is performed by using an X-ray photoelectron spectroscopy (XPS) instrument with an Al target Kα radiation X-ray source with hν of 1486.6eV. N1s is peaked at 401eV, and the graphite nitrogen area proportion is calculated, which is the mass proportion of graphite nitrogen in the total nitrogen content of the negative electrode material.

[0129] Graphitic nitrogen refers to nitrogen atoms in the form of sp 2 The hybrid state exists in the hexagonal ring structure. The introduction of graphitic nitrogen in graphite or graphite-like coating materials can form an additional π-electron system, enhance the electron transport ability of the material, improve its conductivity, increase the diffusion ability of electrons in the coating layer, and improve the fast charging performance.

[0130] Controlling the mass proportion of graphite nitrogen in the total nitrogen content of the negative electrode active material within the above range can not only enhance the conductivity, but also help to make the total mass proportion of pyridinic nitrogen and pyrrolic nitrogen in the total nitrogen content 30%-80%, thereby improving the fast charging performance of the secondary battery.

[0131] Exemplarily, the mass proportion of graphite nitrogen in the total nitrogen content of the negative electrode active material is any value among 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30% or between any two values.

[0132] In some embodiments, the negative electrode active material satisfies at least one of (a1)-(a5):

[0133] (a1) The volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm;

[0134] For the volume particle size distribution Dv50 of the negative electrode active material, the powder scraped from the surface of the negative electrode plate can be roasted to remove the binder, conductive agent, etc., and the negative electrode active material can be obtained as a sample for laser diffraction testing, wherein the laser diffraction method includes the use of: Equipment model: Malvern 2000 (MasterSizer2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO13320:2009, specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is guaranteed to be 8-12% shading), add 20ml of deionized water, and at the same time exceed 5min (53KHz / 120W) to ensure that the sample is completely dispersed, and then measure the sample according to GB / T19077-2016 / ISO13320:2009 standard. It should be noted that when the negative electrode film layer is composed of the fast-charging negative electrode active material and graphite layered coating, the scraped thickness does not exceed the thickness of the surface layer.

[0135] The volume particle size distribution Dv50 of the negative electrode active material is within the above range, which is beneficial for the negative electrode plate to maintain the porosity of the negative electrode film layer within the range of 20%-35% when the negative electrode plate is under pressure, and can reduce the loss of energy density caused by excessively high porosity, which is beneficial for the battery to better balance energy density with higher fast charging performance.

[0136] Illustratively, the volume particle size distribution Dv50 of the negative electrode active material is any value of 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm or between any two values.

[0137] (a2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g;

[0138] Specific surface area test: The test method refers to the standard GB / T19587-2004 "Determination of specific surface area of ​​solid substances by gas adsorption BET emission". It can be understood that the average specific surface area of ​​the negative electrode active material is obtained in the test here.

[0139] The specific surface area of ​​the negative electrode active material is controlled within the above range so that it has a larger specific surface area, which is conducive to the adsorption of lithium ions and the improvement of fast charging performance.

[0140] For example, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10.0m 2 / g, 10.5m 2 Any value in / g or between any two values.

[0141] (a3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0142] The thickness of the nitrogen-doped porous carbon layer is well known in the art and can be tested by methods known in the art. For example, a transmission electron microscope (TEM) can be used to measure multiple times, for example, 30 negative electrode active materials can be tested, and the average thickness of the 30 negative electrode active materials can be used as the thickness of the nitrogen-doped porous carbon layer; wherein the thickness of 10 sites at different positions of the nitrogen-doped porous carbon layer of each negative electrode active material is selected as the thickness of the nitrogen-doped porous carbon layer of the negative electrode active material.

[0143] The thickness of the nitrogen-doped porous carbon layer is within the above range, which can improve the overall conductivity and structural stability of the negative electrode active material, while also helping to further increase the shuttle migration speed of active lithium ions in the negative electrode film layer, thereby improving the fast charging performance of the battery.

[0144] Illustratively, the thickness of the nitrogen-doped porous carbon layer is any value of 10 nm, 50 nm, 100 nm, 200 nm, 250 nm, 300 nm, 400 nm, 490 nm, 499 nm, or between any two values.

[0145] (a4) the carbon core comprises at least one of artificial graphite and natural graphite;

[0146] Taking the distinction between natural graphite and artificial graphite in the negative electrode active material as a non-limiting example, natural graphite and artificial graphite can be distinguished by the appearance of the particles; X-ray diffraction (XRD) analysis test can be further performed. In the XRD spectrum, the characteristic peak near 2θ26.5° is very sharp and has a high intensity, which is natural graphite; the characteristic peak near 2θ26.5° is relatively wide and weak in intensity, which is artificial graphite. Alternatively, Raman spectroscopy test analysis can be used to analyze hard carbon based on the characteristic peak information of the carbon component in the spectrum (such as the intensity ratio of D peak / G peak, ID / G). Both D peak and G peak are Raman characteristic peaks of carbon atom crystal. D peak represents the defects of carbon atom crystal. The more defects there are, the greater the intensity of D peak is. The intensity of D peak can reflect the content of amorphous (turbostratified stacking) area. G peak represents the in-plane stretching vibration of sp2 hybridization of carbon atom. The intensity of G peak can reflect the content of graphitized (layered structure) area. As the disorder degree of carbon atoms increases, the intensity ratio of D peak to G peak also increases. According to the difference in the intensity of D peak and G peak of Raman spectrum, it can also be used to distinguish natural graphite from artificial graphite.

[0147] Exemplarily, the carbon core is artificial graphite.

[0148] The nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of the secondary battery.

[0149] (a5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

[0150] The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, including: the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, or the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, at this time, the nitrogen-doped porous soft carbon layer and the nitrogen-doped porous hard carbon layer are stacked, at this time, the nitrogen-doped porous soft carbon layer can be located between the nitrogen-doped porous hard carbon layer and the carbon core, or, the nitrogen-doped porous hard carbon layer can be located between the nitrogen-doped porous soft carbon layer and the carbon core.

[0151] Exemplarily, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer or a nitrogen-doped porous hard carbon layer.

[0152] In some embodiments, the carbon core includes secondary graphite particles, and the volume particle size distribution Dv50 of the secondary graphite particles is 9 μm-22 μm; or,

[0153] The carbon core includes graphite single particles, and the volume particle size distribution Dv50 of the graphite single particles is 5μm-10μm.

[0154] Secondary graphite particles refer to the secondary graphite particles obtained by mixing artificial graphite powder with a binder, granulating, carbonizing, and graphitizing. Secondary graphite particles have rich orientations, but poor structural stability. Therefore, using secondary graphite particles within the above particle size range as the carbon core is beneficial to improving the compaction density of the negative electrode sheet and facilitating the infiltration of the core by the electrolyte, so that the secondary battery has both better energy density and fast charging performance.

[0155] Illustratively, the volume particle size distribution Dv50 of the secondary graphite particles is any value of 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 20 μm, 22 μm or between any two values.

[0156] A single graphite particle refers to a single graphite particle, which is a primary graphite particle. It has a stable structure but poor wettability. Therefore, selecting a particle size within the above-mentioned smaller range is beneficial to improving the fast charging performance of secondary batteries while improving the cycle performance.

[0157] Illustratively, the volume particle size distribution Dv50 of the graphite single particles is any value of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or between any two values.

[0158] In some embodiments, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2):

[0159] (b1) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-9.0m 2 / g;

[0160] Within the above-mentioned specific surface area range, the negative electrode active material composed of a nitrogen-doped porous soft carbon layer covering a carbon core has a better porosity, which is beneficial to improving the contact angle of the negative electrode active material, enhancing the wettability, and improving the battery fast charging performance and cycle performance.

[0161] For example, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9.0m 2 Any value in / g or between any two values.

[0162] (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, the micropores and the mesopores are at least partially interconnected, the volume of the micropores accounts for 0-25% of the total pore volume, and / or the volume of the mesopores accounts for 63%-90% of the total pore volume.

[0163] Controlling the proportion of the volume of micropores to the total pore volume to be 0-25%, and / or the proportion of the volume of mesopores to the total pore volume to be 63%-90%, is not only beneficial to improving the pore structure of the nitrogen-doped porous soft carbon layer, but also beneficial to improving the contact angle of the negative electrode active material, improving the wettability, improving the battery fast charging performance and cycle performance, and the lower micropore content has a weaker effect on the deterioration of the first efficiency.

[0164] Illustratively, the ratio of the volume of micropores to the total pore volume is any value among 0, 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, or between any two values.

[0165] Exemplarily, the volume of mesopores accounts for any proportion of the total pore volume of 63%, 65%, 68%, 70%, 73%, 75%, 77%, 80%, 82%, 85%, 87%, 90%, or between any two values.

[0166] In some embodiments, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1)-(c2):

[0167] (c1) The specific surface area of ​​the negative electrode active material is 4.0 m 2 / g-10.5m 2 / g;

[0168] Within the above-mentioned specific surface area range, the negative electrode active material composed of a nitrogen-doped porous hard carbon layer covering a carbon core has a better porosity, which is beneficial to improving the contact angle of the negative electrode active material, enhancing the wettability, and improving the battery fast charging performance and cycle performance.

[0169] For example, the specific surface area of ​​the negative electrode active material is 4 m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9.0m 2 / g, 10.0m 2 / g, 10.5m 2 Any value in / g or between any two values.

[0170] (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, and the micropores and mesopores are at least partially interconnected. The volume of the micropores accounts for 25%-50% of the total pore volume, and / or the volume of the mesopores accounts for 40%-85% of the total pore volume.

[0171] The volume of micropores accounts for 25%-50% of the total pore volume, and / or the volume of mesopores accounts for 40%-85% of the total pore volume. Improving the pore structure of the nitrogen-doped porous hard carbon layer is beneficial to improving the contact angle of the negative electrode active material, improving the wettability, improving the fast charging performance and cycle performance of the battery, and the lower micropore content has a weaker effect on the deterioration of the first effect.

[0172] Illustratively, the ratio of the volume of micropores to the total pore volume is any value among 25%, 30%, 35%, 40%, 45%, 50%, or between any two values.

[0173] Exemplarily, the volume of mesopores accounts for any proportion of the total pore volume of 40%, 45%, 50%, 55%, 60%, 65%, 68%, 70%, 73%, 75%, 77%, 80% or between any two values.

[0174] In some embodiments, the single surface density of the negative electrode film layer is 100 mg / cm 2 -200mg / cm 2 .

[0175] In the present application, the single-sided surface density of the negative electrode film layer has a well-known meaning in the art and can be tested by methods known in the art. For example, take a pole piece that has been coated on one side and cold pressed (if it is a pole piece coated on both sides, the film layer on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, and record it as M1. Then wipe off the film layer of the pole piece weighed above, weigh the weight of the current collector, and record it as M0. Single-sided surface density of the film layer = (M1-M0) / S1. In order to ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0176] The single-surface surface density of the negative electrode film layer is within the above range, which is beneficial to the diffusion of lithium ions in the negative electrode film layer and can effectively inhibit lithium precipitation, and can more effectively improve the fast charging performance and cycle performance of the secondary battery.

[0177] For example, the surface density of the negative electrode film layer is 100 mg / cm 2 、110mg / cm 2 、120mg / cm 2 、130mg / cm 2 、140mg / cm 2 、150mg / cm 2、160mg / cm 2 、170mg / cm 2 、180mg / cm 2 、190mg / cm 2 , 200mg / cm 2 Any value in or between any two values.

[0178] In some embodiments, the compaction density of the negative electrode film layer is 1.3 g / cm 3 -1.8g / cm 3 .

[0179] The compaction density of the electrode sheet is a well-known meaning in the art and can be tested by methods known in the art. Remove the negative electrode sheet from the lithium-ion battery, take a certain area of ​​the negative electrode sheet, and measure the mass and thickness of the negative electrode sheet and the negative electrode collector after removing the negative electrode film layer. Calculate the compaction density of the negative electrode sheet according to the following formula. Compaction density of negative electrode sheet = (mass of negative electrode sheet - mass of negative electrode collector) / [(thickness of negative electrode sheet - thickness of negative electrode collector) × area of ​​negative electrode sheet].

[0180] The negative electrode film layer is at a relatively high compaction density, that is, the secondary battery can effectively improve the energy density of the secondary battery on the basis of having fast charging performance, which is conducive to high-rate charging.

[0181] For example, the compaction density of the negative electrode film layer is 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 Any value in or between any two values.

[0182] In some embodiments, the porosity of the negative electrode film layer is 20%-35%.

[0183] The test method for the porosity of the negative electrode film layer in the present application includes: discharging the secondary battery to the discharge cut-off voltage, disassembling to obtain the negative electrode plate; soaking the negative electrode plate with DMC (dimethyl carbonate), washing with deionized water and ethanol, and drying the washed negative electrode plate. The porosity of the positive electrode film layer is measured by the volume method, and the porosity of the negative electrode film layer is calculated by the volume of the liquid immersed in the pores of the negative electrode film layer. The test steps are as follows: put the negative electrode plate sample into a measuring cylinder, add n-butanol liquid to immerse the negative electrode plate, and record the volume V1 at this time. After standing for 6 hours, the above n-butanol liquid is immersed in the negative electrode film layer, and the volume change ΔV is read. Take out the negative electrode plate, scrape off the negative electrode film layer after drying, and measure the volume of the negative electrode current collector as V2. Calculate the porosity δ of the negative electrode film layer, where δ = ΔV / (V1-V2).

[0184] Controlling the porosity of the negative electrode film layer to 20%-35% is beneficial for making the negative electrode film layer more fully infiltrated with the electrolyte during the cycle process, which is beneficial to improving fast charging and cycle performance and facilitating charging and discharging at a high rate.

[0185] Exemplarily, the porosity of the negative electrode film layer is any value of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35% or between any two values.

[0186] In some embodiments, the absorption rate of the negative electrode plate for the E324 electrolyte is 0.5 mg / s 1 / 2 -4mg / s 1 / 2 .

[0187] The liquid absorption rate of the negative electrode plate can reflect the ability of the negative electrode plate to be wetted in the electrolyte. In this application, the test method of the liquid absorption rate includes: disassembling the battery cell to remove the negative electrode plate, drying the negative electrode plate and cutting it into 20mm×10mm plates, the thickness of the test plate is D, and it is fixed on the sample table, and the E324 electrolyte is dripped and timed with a stopwatch; the weight increase and time are recorded; the liquid absorption rate of the plate is calculated by the change of weight over time. The higher the liquid absorption rate, the faster the infiltration speed.

[0188] The E324 electrolyte includes: the solvent is composed of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:3:6, and the lithium salt is 1.0M LiPF 6 The additives are 1% by mass of vinylene carbonate (VC) added to the electrolyte, and 1% by mass of fluoroethylene carbonate (FEC) added to the electrolyte.

[0189] The above-mentioned negative electrode plate has a high liquid absorption rate, which can improve the wetting efficiency of the electrolyte on the negative electrode plate, improve the ion transmission path, reduce the interface resistance, and improve the fast charging performance of the secondary battery.

[0190] For example, the absorption rate of the negative electrode plate for the E324 electrolyte is 0.5 mg / s 1 / 2 、1.0mg / s 1 / 2 , 1.5mg / s 1 / 2 , 2.0mg / s 1 / 2 , 2.5mg / s 1 / 2 、3.0mg / s 1 / 2 、3.5mg / s 1 / 2 , 4.0mg / s 1 / 2 Any value of or between any two values.

[0191] A second aspect of the embodiments of the present application provides an electrical device, which includes the secondary battery provided by the first aspect of the present application.

[0192] A third aspect of the present application provides a negative electrode active material, the negative electrode active material comprising a carbon core and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, the nitrogen-doped porous carbon layer comprising pyrrolic nitrogen, pyridinic nitrogen and mesopores;

[0193] Among them, the volume proportion of mesopores in the total pore volume of the negative electrode active material is 40%-90%;

[0194] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by weight, and the pyrrolic nitrogen and pyridinic nitrogen together account for 30%-80% by weight of the total nitrogen content in the negative electrode active material.

[0195] For negative electrode active materials, according to the pore size, the pore size of mesopores is 2nm≤≤50nm, which is more conducive to the transmission of solvated lithium ions than micropores, and the mesopore content is positively correlated with the wettability. However, if the content is too large, the mechanical properties are poor, and the kinetic properties and cycle performance are easily deteriorated due to breakage. Therefore, the content of mesopores is controlled within the above range. On the basis of the nitrogen-doped carbon coating having better mechanical properties, it not only provides more lithium ion embedding channels and shortens the lithium ion transmission distance, but also provides multi-dimensional open permeation channels, enhances the wettability of the electrolyte, and makes it easier for the solvated lithium ions in the electrolyte to diffuse to the surface of the graphite particles, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, and accelerate the liquid phase mass transfer step in the electrolyte phase.

[0196] The total nitrogen content in the negative electrode active material is controlled to account for 0.4%-3% by weight, and the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%-80% by weight. High nitrogen doping is used to improve the adsorption capacity of the negative electrode active material for lithium ions, and nitrogen doping is used to enrich pyrrolic nitrogen and pyridinic nitrogen. On the one hand, pyrrolic nitrogen and pyridinic nitrogen are used to induce the formation of SEI during the chemical film formation process, forming a SEI with more inorganic components-lithium nitride (LiN). 3 N), this inorganic component SEI is compared with Li 2 CO 3 The higher adsorption energy makes it easier for lithium ions to diffuse to the surface. At the same time, this type of inorganic component SEI has a lower desolvation energy barrier, which accelerates the reduction of the transfer impedance of lithium ions in the coating layer and accelerates the desolvation step of the solvated lithium ions. On the other hand, pyridinic nitrogen and pyrrolic nitrogen have lone pairs of electrons in their heterocyclic structures, which makes them show higher reactivity in electrochemical and catalytic applications. They can more efficiently adsorb lithium ions during charging and discharging, reduce the desolvation energy barrier, and reduce Li + The mass transfer resistance is reduced and the lithium ion diffusion capacity of the coating layer is improved, thereby accelerating the diffusion of desolvated lithium ions in the graphite coating layer.

[0197] It is understandable that, based on the above reasons, if the total content of pyrrole nitrogen and pyridinic nitrogen, or the total nitrogen content is too low, the effect of improving the desolvation rate of solvated lithium ions and the lithium ion diffusion rate will be limited. If it is too large, it will lead to SEI thickening, affecting the initial effect of the secondary battery and the long-term performance of the secondary battery. Therefore, in this application, the total nitrogen content in the negative electrode active material is controlled to account for 0.4%-3% by mass, and the mass proportion of pyrrole nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%.

[0198] In summary, the negative electrode active material provided by the present application has high nitrogen doping while taking into account high mesoporous content, and the high nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyridinic nitrogen. Therefore, the high mesoporous content is utilized to effectively improve the wettability of the negative electrode active material and shorten the lithium ion transmission distance, and the high nitrogen doping is utilized to improve the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrolic nitrogen and pyridinic nitrogen are utilized to improve the lithium ion diffusion rate, and the introduction of defect sites to improve the wettability of the negative electrode active material. The combined effect of the three improves the wettability of the negative electrode active material and constructs a migration path for rapid transmission of lithium ions, thereby effectively improving the fast charging performance of the secondary battery.

[0199] Exemplarily, the volume fraction of mesopores in the total pore volume of the negative electrode active material is any one of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90%, or between any two values.

[0200] Illustratively, the mass percentage of the total nitrogen content in the negative electrode active material is any value among 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0% or between any two values.

[0201] Exemplarily, the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or between any two values.

[0202] In some embodiments, the negative electrode active material satisfies at least one of (d1)-(d5):

[0203] (d1) The volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm;

[0204] The volume particle size distribution Dv50 of the negative electrode active material is within the above range, which is beneficial for the negative electrode plate to maintain the porosity of the negative electrode film layer within the range of 20%-35% when the negative electrode plate is under pressure, and can reduce the loss of energy density caused by excessively high porosity, which is beneficial for the battery to better balance energy density with higher fast charging performance.

[0205] Illustratively, the volume particle size distribution Dv50 of the negative electrode active material is any value of 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm or between any two values.

[0206] (d2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g;

[0207] The specific surface area of ​​the negative electrode active material is controlled within the above range so that it has a larger specific surface area, which is conducive to the adsorption of lithium ions and the improvement of fast charging performance.

[0208] For example, the specific surface area of ​​the negative electrode active material is 1.0 m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10.0m 2 / g, 10.5m2 Any value of / g or between any two values.

[0209] (d3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0210] The thickness of the nitrogen-doped porous carbon layer is within the above range, which can improve the overall conductivity and structural stability of the negative electrode active material, while also helping to further increase the shuttle migration speed of active lithium ions in the negative electrode film layer, thereby improving the fast charging performance of the battery.

[0211] Illustratively, the thickness of the nitrogen-doped porous carbon layer is any value of 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 490 nm, and 499 nm, or is between any two values.

[0212] (d4) the carbon core comprises at least one of artificial graphite and natural graphite;

[0213] The nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of the secondary battery.

[0214] Exemplarily, the carbon core is artificial graphite.

[0215] The nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of the secondary battery.

[0216] (d5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

[0217] The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, including: the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, or the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, at this time, the nitrogen-doped porous soft carbon layer and the nitrogen-doped porous hard carbon layer are stacked, at this time, the nitrogen-doped porous soft carbon layer can be located between the nitrogen-doped porous hard carbon layer and the carbon core, or, the nitrogen-doped porous hard carbon layer can be located between the nitrogen-doped porous soft carbon layer and the carbon core.

[0218] A fourth aspect of the present application provides a method for preparing a negative electrode active material, which includes:

[0219] After mixing the high nitrogen polymer and the carbon core, carbonization is carried out in an inert atmosphere;

[0220] The total nitrogen content of the high nitrogen polymer is ≥0.8% by mass. The high nitrogen polymer includes pyrrolic nitrogen and pyridinic nitrogen. The mass content of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the high nitrogen polymer is 40%-90%.

[0221] In the present application, a high-nitrogen polymer is selected as a carbon source and a nitrogen source, and a nitrogen-doped carbon coating layer can be directly formed on the surface of the carbon core during the carbonization process, which is conducive to more uniform nitrogen doping and mesopore distribution.

[0222] In the present application, by selecting a high-nitrogen polymer as a carbon source and a nitrogen source, and by controlling the total nitrogen mass content in the high-nitrogen polymer to be ≥0.8%, it is beneficial for part of the nitrogen in the high-nitrogen polymer to decompose and overflow during carbonization to form pores in the formed carbon layer to form mesopores, micropores, etc., which is beneficial for the volume proportion of the mesopores in the total pore volume of the negative electrode active material after carbonization to be 40%-90%, and the remaining nitrogen remains in the carbon layer for nitrogen doping, which is beneficial for the total nitrogen content in the negative electrode active material to reach a mass proportion of 0.4%-3%; at the same time, since the mass proportion of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the high-nitrogen polymer is 40%-90%, pyridine nitrogen and pyrrole nitrogen are more likely to be formed during carbonization, and the content of pyridine nitrogen and pyrrole nitrogen in the carbon layer is high, which is beneficial for the mass proportion of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material to reach 30%-80%.

[0223] That is, the preparation method provided by the present application selects a high-nitrogen polymer rich in pyridinic nitrogen and pyrrolic nitrogen as a carbon source and a nitrogen source, directly mixes it with a carbon core and then carbonizes it, which is beneficial to the preparation process, part of the nitrogen in the high-nitrogen polymer overflows to increase the mesopores of the negative electrode active material, and the remaining nitrogen is doped in the formed carbon layer and tends to form pyridinic nitrogen and pyrrolic nitrogen. Not only is the nitrogen doping and mesopore distribution in the prepared negative electrode active material more uniform, but the mesopore content and nitrogen doping amount in the negative electrode active material are also simultaneously improved, and the nitrogen doping mainly exists in the form of pyrrolic nitrogen and pyrrolic nitrogen. The high mesopore content is used to effectively improve the wettability of the negative electrode active material, so that the solvated lithium ions can reach the surface of the carbon core more efficiently, the high nitrogen doping is used to improve the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrolic nitrogen and pyridinic nitrogen are used to improve the desolvation rate of the solvated lithium ions and the lithium ion diffusion rate. The combined effect of the three accelerates the kinetic process during the charging process of the secondary battery and effectively improves the fast charging performance of the secondary battery.

[0224] In some embodiments, the preparation method satisfies at least one of (e1)-(e3):

[0225] (e1) the high nitrogen polymer includes at least one of a high nitrogen asphalt and a high nitrogen copolymer;

[0226] The high nitrogen asphalt and high nitrogen copolymer can both be used as nitrogen source and carbon source to prepare the negative electrode active material.

[0227] High nitrogen asphalt is mainly derived from petroleum asphalt, in which the nitrides are derived from natural heterocyclic nitrogen compounds in crude oil. During the oil processing process, these nitrides can be retained or further enriched to form high nitrogen asphalt. Exemplarily, a heavy petroleum asphalt is selected as high nitrogen asphalt, which is the most common type of nitrogen-containing asphalt, directly derived from the refining process of crude oil, and heavy petroleum asphalt contains various heterocyclic nitrogen compounds, such as pyridine, quinoline, indole and its derivatives.

[0228] It should be noted that in order to achieve more uniform coating, when the high nitrogen polymer is high nitrogen asphalt, the two can be directly mixed. In the process of heating to the carbonization temperature, the high nitrogen asphalt softens and coats the surface of the carbon core, and then the carbonization temperature is maintained for carbonization. When the high nitrogen polymer is a high nitrogen copolymer, the high nitrogen copolymer can be dissolved in a solvent in advance, mixed with the carbon core liquid phase, and then the temperature is raised to the carbonization temperature for carbonization.

[0229] (e2) The carbonization temperature is 700°C-1300°C, and the carbonization time is 6h-15h;

[0230] The holding time and holding temperature affect the depth of carbonization treatment. Controlling the carbonization temperature and time within the above range is beneficial to having enough nitrogen remaining in the carbon layer after carbonization on the one hand, and is also beneficial to the full carbonization of high-nitrogen polymers on the other hand, reducing the influence of residual non-carbon elements and organic residues on the purity and long-term performance of the material, and is also beneficial to the formation of an ordered graphite structure. The finished product has good conductivity and mechanical strength, as well as good pore structure, which improves wettability.

[0231] Exemplarily, the carbonization temperature is any one of 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h or between any two values.

[0232] Illustratively, the carbonization time is any one of 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., and 1000° C., or between any two values.

[0233] Optionally, the temperature is increased to the carbonization temperature at a heating rate of 2°C / min-20°C / min.

[0234] Exemplarily, the heating rate is any value of 2°C / min, 5°C / min, 7°C / min, 10°C / min, 12°C / min, 15°C / min, 17°C / min, 20°C / min or between any two values.

[0235] (e3) The mass ratio of the high nitrogen polymer to the carbon core is 100:2-20.

[0236] The mass ratio of the high nitrogen polymer to the carbon core is 100:2-20, which is conducive to the carbon coating layer being fully coated on the surface of the carbon core and avoids the carbon coating layer formed by carbonization being too thick to deteriorate the fast charging performance of the secondary battery.

[0237] Exemplarily, the mass ratio of the high nitrogen polymer to the carbon core is any one of 100:2, 100:5, 100:7, 100:10, 100:12, 100:15, 100:17, 100:20 or between any two values.

[0238] In some embodiments, the high nitrogen polymer is a high nitrogen copolymer;

[0239] Wherein, the nitrogen mass content in the high nitrogen copolymer is 1%-5%; and / or,

[0240] The carbonization temperature is 1000°C-1100°C; and / or,

[0241] High nitrogen copolymers include acrylic acid-acrylonitrile copolymers.

[0242] The acrylic acid-acrylonitrile copolymer can introduce more nitrogen through the copolymerization of two or more monomers, and has a high nitrogen content, which is beneficial for preparing the negative electrode active material of the present application.

[0243] Under the condition of selecting the high nitrogen polymer as the high nitrogen copolymer, by controlling the nitrogen mass content and / or the insulation temperature within the above range, it is beneficial to carbonize the high nitrogen copolymer to form a nitrogen-doped porous hard carbon coating layer coated on the surface of the carbon core. Combined with the insulation time, the carbonization depth is within a suitable range, so as to obtain a negative electrode active material that has both high mesoporous content and high nitrogen doping, which is beneficial to improving the fast charging performance of the battery.

[0244] Exemplarily, the insulation temperature is any value of 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C, 1100°C or between any two values.

[0245] In some embodiments, the high nitrogen polymer is high nitrogen asphalt;

[0246] Wherein, the nitrogen content of high nitrogen asphalt is 0.8%-4% by mass; and / or,

[0247] The insulation temperature is 900℃-1300℃.

[0248] When the high-nitrogen polymer is selected as high-nitrogen asphalt, by controlling the nitrogen mass content and / or the insulation temperature within the above range, it is beneficial to carbonize the high-nitrogen asphalt to form a nitrogen-doped porous soft carbon coating layer coated on the surface of the carbon core. Combined with the insulation time, the carbonization depth is within an appropriate range, and a negative electrode active material that has both high mesoporous content and high nitrogen doping is obtained, which is beneficial to improving the fast charging performance of the battery.

[0249] Exemplarily, the mass content of nitrogen in high nitrogen asphalt is any value of 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0% or between any two values.

[0250] Exemplarily, the insulation temperature is any one of 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., 1000° C. or between any two values.

[0251] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0252] [Secondary battery]

[0253] A second aspect of the embodiments of the present application provides a secondary battery. The present application has no particular limitation on the type of the secondary battery, for example, the secondary battery may be a lithium-ion battery.

[0254] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0255] The present application has no particular restrictions on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte). A secondary battery using an electrolyte, and some secondary batteries using a solid electrolyte.

[0256] [Positive electrode]

[0257] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0258] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0259] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0260] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may adopt a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (Also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (Also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (Also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (Also referred to as NCM811 )), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O 2 ), and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0261] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for a lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0262] In some embodiments, by way of example, the positive electrode active material for a lithium-ion battery may include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2 、LiFePO 4 and LiMnPO 4 One or more of .

[0263] In the present application, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification of the positive electrode active materials.

[0264] As an optional technical method of the present application, the polyanionic compound can be Li 1+x Mn 1-y A y P 1-z R z O 4 ; wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0265] As an optional technical method of the present application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n , wherein A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from the group consisting of B, S, Si, and N; D includes one or more elements selected from the group consisting of S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0266] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.

[0267] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0268] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0269] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0270] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0271] [Negative electrode]

[0272] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.

[0273] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0274] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0275] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0276] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0277] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0278] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0279] [Electrolytes]

[0280] The electrolyte conducts ions between the positive electrode and the negative electrode.

[0281] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0282] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0283] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0284] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0285] [Isolation film]

[0286] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0287] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0288] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0289] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0290] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0291] In the present application, a secondary battery may refer to a single battery cell, or it may refer to a single physical module including multiple battery cells to provide higher voltage and capacity, which may be in the form of a battery pack, a battery module, etc.

[0292] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0293] In some embodiments, reference Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0294] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0295] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0296] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0297] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0298] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0299] In addition, the present application also provides an electrical device, which includes a secondary battery (at least one of a battery cell, a battery module, or a battery pack) provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0300] As an electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0301] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0302] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0303] Example

[0304] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0305] Example 1

[0306] [Negative electrode active material]

[0307] High nitrogen asphalt and artificial graphite are mixed in a mass ratio of 10:1, and the temperature is increased to 1050°C at a heating rate of 10°C / min in an argon atmosphere and kept for 9 hours to obtain a negative electrode active material. The negative electrode active material includes an artificial graphite core and a nitrogen-doped porous carbon layer coated on the surface thereof.

[0308] Among them, the artificial graphite is secondary particle artificial graphite.

[0309]

Negative electrode

[0310] The above-mentioned negative electrode active material, thickener (carboxymethyl cellulose), binder (SBR), and conductive agent are mixed in a mass ratio of 97.3:1.2:0.8:0.7, and mixed with solvent (deionized water) under certain parameters in a vacuum mixer to prepare negative electrode slurry, which is then evenly coated on the negative electrode current collector copper foil. The negative electrode current collector coated with the negative electrode slurry is dried at room temperature and then transferred to an oven for drying, and then cold pressed and cut to obtain negative electrode sheets. Among them, the single-sided surface density of the negative electrode film layer is 160mg / cm 2 .

[0311]

Positive electrode

[0312] The positive electrode active material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), conductive agent (SuperP), binder (PVDF), etc. are mixed in a ratio of 96:2:2, a solvent (NMP) is added, and the system is stirred under the action of a vacuum mixer until the system becomes a uniform and transparent state to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil; the positive electrode collector coated with the positive electrode slurry is dried at room temperature and then transferred to an oven for drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0313]

Isolation film

[0314] A polyethylene film with a thickness of 12 μm was selected.

[0315]

Electrolyte

[0316] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then the fully dried lithium salt LiPF 6 It is dissolved in a mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0317]

Secondary battery

[0318] The prepared positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is obtained by winding; the electrode assembly is placed in a shell, and the electrolyte is injected after baking, and a secondary battery is obtained after standing, hot and cold pressing, formation, aging, shaping, capacity testing and other processes.

[0319] Examples 2-16 and Comparative Examples 1-2

[0320] The difference between the above-mentioned embodiment and the comparative example mainly lies in the negative electrode active material and the negative electrode plate. The specific relevant parameters are shown in Table 1 and Table 2 below.

[0321] The only difference between Example 6 and Example 1 is that the artificial graphite selected in the preparation process is a single particle of artificial graphite. Due to the different selection of artificial graphite, the parameters of the prepared negative electrode active material change as shown in Table 1 and Table 2.

[0322] Among them, the difference between Comparative Example 1 and Example 1 is that: based on the total nitrogen content in the high nitrogen precursor is only 0.40%, the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the high nitrogen precursor is 74%, resulting in the parameters of the prepared negative electrode active material changing as shown in Table 1 and Table 2.

[0323] The only difference between Comparative Example 2 and Example 1 is that the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the high-nitrogen precursor is too small, resulting in changes in the parameters of the prepared negative electrode active material as shown in Tables 1 and 2.

[0324] Table 1 Differentiating parameters of each embodiment and comparative example

[0325]

[0326]

[0327] Table 2 Differentiating parameters of each embodiment and comparative example

[0328]

[0329]

[0330] In addition, the secondary batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests.

[0331] Fast charging performance test: The batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour), specifically including: at 35°C, the battery was charged at a constant current of 1C to a voltage of 4.4V, then charged at a constant voltage to a current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to a voltage of 2.8V, and its actual capacity was recorded as C0.

[0332] Then the battery is charged with a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 in sequence to a full battery charge cutoff voltage of 4.4V or a negative electrode cutoff potential of 0V (whichever is reached first). After each charge is completed, it is necessary to discharge with 1C0 to a full battery discharge cutoff voltage of 2.8V. The corresponding negative electrode potential when charged to 10%, 20%, 30%, ..., 80% SOC (State of Charge, when "SOC = 0" indicates that the battery is fully discharged, and when "SOC = 100%" indicates that the battery is fully charged) at different charge rates is recorded, and different SOC states are plotted. The charge rate negative electrode potential curve under different SOC states is obtained by linear fitting, and the charge rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. The charge rate is the charging window under the SOC state, which is recorded as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC respectively. The charging time T of the battery from 10%SOC to 80%SOC is calculated according to the formula (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%, in min. The shorter the time, the better the fast charging performance of the battery.

[0333] Fast charge cycle performance test: Step charge at the charge rate at each SOC obtained from the fast charge performance test, specifically: C10% SOCCC to 10% SOC, C20% SOCCC to 20% SOC, C30% SOCCC to 30% SOC, C40% SOCCC to 40% SOC, C50% SOCCC to 50% SOC, C60% SOCCC to 60% SOC, C70% SOCCC to 70% SOC, C80% SOCCC to 80% SOC, 0.33C to 100% SOC, 0.33CDC to 2.5V, record the number of cycles when Fading to 80% SOH. Among them, C10% SOC represents the charge rate at 10% SOC, CC represents constant current charging, and DC represents.

[0334] The results are shown in Table 3.

[0335] Table 3: Performance test results of examples and comparative examples

[0336]

[0337]

[0338] According to Table 1, Table 2 and Table 3, it can be seen that the secondary battery provided in the embodiment of the present application has a low charging time from 10% SOC to 80% SOC and has good fast charging performance.

[0339] Among them, according to Example 1 and Comparative Example 1, it can be known that since the nitrogen content in the precursor is too low, the residual total nitrogen content of the prepared negative electrode active material is too low, and the overflow portion is small, resulting in a large contact angle of the negative electrode active material, resulting in a long charging time for the secondary battery from 10% SOC to 80% SOC, a low number of cycles at 45°C 80% SOH, and poor fast charging performance.

[0340] According to Example 2 and Comparative Example 2, it can be seen that the charging time of the secondary battery from 10% SOC to 80% SOC is long and the fast charging performance is poor, mainly because the mass proportion of pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is too small.

[0341] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: It includes a negative electrode plate, wherein the negative electrode plate includes a negative electrode film layer; The negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a carbon core, and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, the nitrogen-doped porous carbon layer includes pyrrolic nitrogen, pyridinic nitrogen and mesopores; Wherein, the volume proportion of the mesopores in the total pore volume of the negative electrode active material is 40%-90%; The total nitrogen content in the negative electrode active material accounts for 0.4% to 3% by weight, and the pyrrolic nitrogen and the pyridinic nitrogen together account for 30% to 80% by weight of the total nitrogen content in the negative electrode active material.

2. The secondary battery according to claim 1, characterized in that: The contact angle of the negative electrode active material is 10°-38.5°.

3. The secondary battery according to claim 1 or 2, characterized in that: The nitrogen-doped porous carbon layer contains micropores and macropores, the micropores, the macropores and the mesopores are at least partially interconnected, and the total volume of the micropores and the macropores accounts for 10%-60% of the total pore volume of the negative electrode active material.

4. The secondary battery according to any one of claims 1 to 3, characterized in that: The mass proportion of the pyrrolic nitrogen in the total nitrogen content of the negative electrode active material is 12%-40%; and / or the mass proportion of the pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 15%-45%.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The mass percentage of the pyrrolic nitrogen and the pyridinic nitrogen in the negative electrode active material is 0.3%-0.9%; and / or, The mass percentage of pyrrolic nitrogen in the negative electrode active material is 0.1%-0.4%; and / or, The mass proportion of the pyridinic nitrogen in the negative electrode active material is 0.2%-0.5%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The nitrogen-doped porous carbon layer comprises graphitic nitrogen and oxynitride; The mass proportion of the graphite nitrogen in the total nitrogen content of the negative electrode active material is 10%-30%.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: The negative electrode active material satisfies at least one of (a1) to (a5): (a1) the volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm; (a2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g; (a3) the thickness of the nitrogen-doped porous carbon layer is ≤500 nm; (a4) the carbon core comprises at least one of artificial graphite and natural graphite; (a5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

8. The secondary battery according to any one of claims 1 to 7, characterized in that: The carbon core comprises secondary graphite particles, and the volume particle size distribution Dv50 of the secondary graphite particles is 9 μm-22 μm; or, The carbon core includes single graphite particles, and the volume particle size distribution Dv50 of the single graphite particles is 5 μm-10 μm.

9. The negative electrode active material according to any one of claims 1 to 8, characterized in that: The nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2): (b1) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-9.0m 2 / g; (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, the micropores and the mesopores are at least partially interconnected, the volume of the micropores accounts for 0-25% of the total pore volume, and / or the volume of the mesopores accounts for 63%-90% of the total pore volume.

10. The negative electrode active material according to any one of claims 1 to 9, characterized in that: The nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1) to (c3): (c1) The specific surface area of ​​the negative electrode active material is 4.0 m 2 / g-10.5m 2 / g; (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, the micropores and the mesopores are at least partially interconnected, the volume of the micropores accounts for 25%-50% of the total pore volume, and / or the volume of the mesopores accounts for 40%-85% of the total pore volume.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The single surface density of the negative electrode film layer is 100 mg / cm 2 -200mg / cm 2 and / or, The compaction density of the negative electrode film layer is 1.3 g / cm 3 -1.8g / cm 3 , and / or, The porosity of the negative electrode film layer is 20%-35%.

12. The secondary battery according to any one of claims 1 to 11, characterized in that: The absorption rate of the negative electrode plate for E324 electrolyte is 0.5 mg / s 1 / 2 -4mg / s 1 / 2 .

13. An electrical device, characterized in that: A secondary battery comprising any one of claims 1 to 12.

14. A negative electrode active material, characterized in that: The negative electrode active material includes a carbon core and a nitrogen-doped porous carbon layer coated on the surface of the carbon core, wherein the nitrogen-doped porous carbon layer includes pyrrolic nitrogen, pyridinic nitrogen and mesopores; Wherein, the volume proportion of the mesopores in the total pore volume of the negative electrode active material is 40%-90%; The total nitrogen content in the negative electrode active material accounts for 0.4% to 3% by weight, and the pyrrolic nitrogen and the pyridinic nitrogen together account for 30% to 80% by weight of the total nitrogen content in the negative electrode active material.

15. The negative electrode active material according to claim 16, characterized in that: The negative electrode active material satisfies at least one of (d1) to (d5): (d1) the volume particle size distribution Dv50 of the negative electrode active material is 7 μm-22 μm; (d2) The specific surface area of ​​the negative electrode active material is 1.0 m 2 / g-10.5m 2 / g; (d3) the thickness of the nitrogen-doped porous carbon layer is ≤500 nm; (d4) the carbon core comprises at least one of artificial graphite and natural graphite; (d5) The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer.

16. A method for preparing a negative electrode active material, characterized in that: include: After mixing the high nitrogen polymer and the carbon core, carbonization is carried out in an inert atmosphere; The total nitrogen content of the high nitrogen polymer is ≥0.8% by mass, and the high nitrogen polymer includes pyrrole nitrogen and pyridinic nitrogen, and the mass proportion of the pyrrole nitrogen and the pyridinic nitrogen in the total nitrogen content of the high nitrogen polymer is 40%-90%.

17. The preparation method according to claim 16, characterized in that: The preparation method satisfies at least one of (e1) to (e3): (e1) the high nitrogen polymer comprises at least one of high nitrogen asphalt and high nitrogen copolymer; (e2) the carbonization temperature is 700° C.-1300° C., and the carbonization time is 6 h-15 h; (e3) The mass ratio of the high nitrogen polymer to the carbon core is 100:2-20.

18. The preparation method according to claim 16 or 17, characterized in that: The high nitrogen polymer is a high nitrogen copolymer; Wherein, the nitrogen mass content of the high nitrogen copolymer is 1%-5%; and / or, The carbonization temperature is 1000°C-1100°C; and / or, The high nitrogen copolymer includes acrylic acid-acrylonitrile copolymer.

19. The preparation method according to claim 16 or 17, characterized in that: The high nitrogen polymer is high nitrogen asphalt; Wherein, the nitrogen mass content of the high nitrogen asphalt is 0.8%-4%; and / or, The carbonization temperature is 900°C-1300°C.

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